1. Field of the Invention
This invention pertains in general to telephone cable networks and, more particularly, to an apparatus and method for assessing signal leakage from the cable networks by exciting the networks with multiple broadband signals.
2. Description of the Related Art
Current developments in the telephone industry show a trend to deploy increased broadband access to a large number of customers throughout the telephone networks. In particular, new technologies permit the telephone industry to deploy a large number of modems that employ signals having frequencies above those anticipated during the deployment of copper-conductor networks, one result of which is a possible increase in signal leakage.
In the United States, the Federal Communications Commission (xe2x80x9cFCCxe2x80x9d) has jurisdiction over all devices that use and could radiate electromagnetic fields. To that end, the FCC has established maximum signal leakage levels permitted for operating electronic equipment. The FCC currently does not provide guidelines to govern the new modem technologies running over existing copper-conductor channels, or loops, in telephone networks. However, regulations may be implemented to require expenditures on the part of network providers to meet existing or new requirements on signal leakage. Assessment of signal leakage in the network would be required.
One technique for signal leakage or coupling assessment involves testing of certain channels of telephone networks by using signals that are representative of the signals intended to be run over the channels. Such intended signals would include audio frequency signals from users of the telephone network as well as the new high frequency signals. Conventional leakage assessment techniques are generally classified as either narrowband or broadband in nature. Narrowband leakage assessment can be either fixed in frequency or swept over a range of frequencies. However, such narrowband techniques typically involve the use of a narrowband detector to limit the noise bandwidth of the detection system and increase the detection sensitivity. For measurements in which the detector is remote from the source, the test source and detector must be synchronized in frequency. Such tuning of the source and detector can be problematic where signal levels may be below the level of the noise, resulting in interference with signals being transmitted in the telephone network.
Known broadband sources include standing wave ratio (xe2x80x9cSWRxe2x80x9d) meters and continuous wave (xe2x80x9cCWxe2x80x9d) sources. For a CW source, test signals are modulated at 1 KHz with either a square or sine wave. A diode detector is used to detect and demodulate the test signals. However, broadband sources used with broadband detection are inappropriate because of the high noise levels at discrete frequencies due to transmitters operating in the band of frequencies of interest. In addition, a conventional broadband leakage assessment only excites one channel of telephone networks at a time, and therefore requires an extended period of time to sweep all the channels of the network.
Accordingly, the present invention is directed to an apparatus and method for assessing signal leakage that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
To achieve these and other advantages, and in accordance with the purpose of the invention as embodied and broadly described, there is provided an apparatus for assessing signal leakage in a telephone network having a plurality of channels that includes a signal generator providing a plurality of test signals to the plurality of channels, and a channel control that connects and disconnects each of the test signals to one of the plurality of channels.
In one aspect of the invention, the apparatus further includes a modulator to modulate one of the test signals wherein the modulator is coupled to one of the plurality of channels.
In another aspect of the invention, the apparatus includes a modulation source coupled to each of the plurality of modulators.
In yet another aspect of the invention, the signal level of the test signals is below the signal level that would cause interference to an audio signal transmitted in the telephone network.
In yet another aspect of the invention, the signal generator includes a clock, an address counter coupled to the clock, and a read-only-memory coupled to the address counter.
Also in accordance with the invention, there is provided an apparatus for assessing signal leakage in a telephone network having a plurality of channels that includes signal generating means for generating a plurality of broadband test signals, a plurality of modulators, each coupled to one of the plurality of channels, for modulating the plurality of test signals, and control means coupled to the plurality of modulators for controlling coupling and decoupling of each of the plurality of channels to the signal generating means.
Further in accordance with the invention, there is provided a method for assessing signal leakage in a telephone network having a plurality of channels that includes generating a plurality of test signals, modulating each of the plurality of test signals with a common modulation source, selectively providing each of the plurality of test signals to the plurality of channels, and assessing test signal leakage on one of the plurality of channels.
In one aspect of the invention, the method simultaneously measures test signals coupled from the other plurality of channels.
In another aspect of the invention, the step of modulating each of the plurality of test signals with a common modulation source comprises a step of coded modulation.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structures and methods particularly pointed out in the written description and claims thereof, as well as the appended drawings.